Long Term Evolution (LTE) systems aim to improve performance by leaps and bounds from 3G cellular systems and under the 3rd Generation Partnership Project (3GPP), advances are being made toward international standardization. LTE systems realize high speed transmission in mobile communication, provide high speed service environments such as high speed image delivery, and are expected to facilitate efficient frequency utilization.
Further, although in existing systems (3G), audio and data communication have been provided by separate communication infrastructures, in LTE systems, movement towards “all IP” integrating audio and data communication to an IP base is intended, whereby completely IP-based systems are expected to be realized by LTE systems, from systems that include conventional circuit switching infrastructure.
Real-time data transmission in LTE systems, similar to Voice over IP (VoIP) in typical wired IP networks, is implemented by RTP/UDP/IP protocols. Consequently, real-time data in LTE systems have large overhead due to the headers appended for each protocol.
In networks that include wireless intervals of limited bandwidth, to improve the bandwidth utilization efficiency of the wireless intervals, a function to compress the protocol headers, which cause overhead, is demanded. This header compression function is expected to be realized in LTE systems.
For example, a technique called Robust Header Compressing (ROHC) included in a Packet Data Convergence Protocol (PDCP) between eNB and UE is expected to implement header compression. Multiple operation modes, each having a different header compression efficiency exist in ROHC (see, for example, Japanese Laid-Open Patent Publication No. 2002-135362).